In recent years, data processing devices and electronic office apparatuses have rapidly spread as a result of technical development in the electronics field.
Wider use of electronic apparatuses entails increased incidences of malfunction and other problems. For example, trouble occurs with electromagnetic waves, in that noises generated from electronic parts affect other apparatuses provided near the electronic parts, leading to occurrence of malfunction caused by electrostaticity. Such trouble has been a serious problem to be solved.
In order to solve the problem, there is demand for materials having excellent conductivity and anti-staticity.
Conventionally, electrically conductive polymer materials which include a polymer material having poor conductivity with conductive fillers or other additives have been widely used.
Generally, metallic fibers, metallic powder, carbon black, and carbon fibers are employed as the aforementioned fillers. When employed as a conductive filler, metallic fibers or metallic powder exhibits an excellent effect of imparting conductivity. However, such a filler raises problems, in that a resin composition containing the filler has poor corrosion resistance and that satisfactory mechanical strength is difficult to attain.
When carbon black is employed as a conductive filler, conductive carbon black products such as Ketjen black, Vulcan XC72, and acetylene black are employed, since addition of such products in a small amount imparts high conductivity. However, dispersibility of these carbon black products in resin is unsatisfactory.
Dispersibility of carbon black incorporated to the resin composition greatly affects the electric conductivity of a resin composition. Therefore, a specific technique for incorporating carbon black in or mixing carbon black with resin is required so as to attain reliable conductivity of the resulting resin composition.
When carbon fibers generally employed as reinforcement materials are employed as conductive fillers, a desired strength and elasticity can be attained. However, in order to impart conductivity to resin, carbon fibers must be charged in the resin at high density, and such high-density charging deteriorates intrinsic properties of the resin.
In addition, when a molded product of complex shape is produced, delocalization of conductive fillers occurs, thereby failing to attain uniformity on conductivity, making the resultant product unsatisfactory.
Carbon fibers of a smaller fiber diameter provide a larger contact area between the fibers and resin at a given amount of the carbon fibers, and therefore, such carbon fibers are expected to impart higher conductivity to the resin.
Japanese kohyo Patent Publication 62-500943 discloses extrafine carbon fibrils having excellent conductivity.
However, the fibrils have poor dispersibility in resin upon mixing, failing to attain satisfactory appearance in molded products.
When a known pigment carbon black is employed as a colorant, a large amount of carbon black must be used for blacking the resin. Such a large amount of carbon black raises problems in terms of dispersibility to resin and surface appearance of molded products.
Japanese patent Application Laid-Open (kokai) No. 3-74465 also discloses a method of adding ultrafine carbon fibrils to resin. This patent document does not describe flame retardancy provided by ultrafine carbon fibrils and never mentions combinatory effect of ultrafine carbon fibrils with a flame retardant.
In addition, flame retardancy provided through the disclosed method is unsatisfactory. Thus, the method cannot be employed for producing a molded product which requires high flame retardancy.
Because of poor dispersibility, carbon fibrils must be added in an increased amount to resin in order to enhance conductivity.
Japanese patent Application Laid-Open (kokai) No. 4-268362 discloses a method of adding conductive carbon to a polycarbonate-polydimethylsiloxane copolymer (PC-PDMS). Since carbon black is used as the conductive carbon, a certain limitation is imposed on the conductivity to be attained. Separation of carbon from the matrix copolymer may also pose a problem during use of the copolymer.
The patent document fails to disclose anything on flame retardancy.
The present invention has been conceived under such circumstances.
An object of invention 1 is to provide a flame-retardant thermoplastic resin composition having electric conductivity. Another object is to provide a molded product of the composition having excellent appearance and enhanced mechanical strength.
An object of invention 2 is to provide an electrically conductive thermoplastic resin composition having high flame retardancy. Another object is to provide a molded product of the composition having excellent appearance and enhanced mechanical strength.
An object of invention 3 is to provide an electrically conductive polycarbonate resin composition having high flame retardancy. Another object is to provide a molded product of the composition having excellent appearance and enhanced mechanical strength.